Thermodynamics of universe with a varying dark energy component

Abstract

We consider a FRW universe filled by a dark energy candidate together with other possible sources which may include the baryonic and non-baryonic matters. Thereinafter, we consider a situation in which the cosmos sectors do not interact with each other. By applying the unified first law of thermodynamics on the apparent horizon of the FRW universe, we show that the dark energy candidate may modify the apparent horizon entropy and thus the Bekenstein limit. Moreover, we generalize our study to the models in which the cosmos sectors have a mutual interaction. Our final result indicates that the mutual interaction between the cosmos sectors may add an additional term to the apparent horizon entropy leading to modify the Bekenstein limit. Relationships with previous works have been addressed throughout the paper. Finally, we investigate the validity of the second law of thermodynamics and its generalized form in the interacting and non-interacting cosmoses.

Energy Definition and Dark Energy: A Thermodynamic Analysis

“…In summary, i) The energy definition and the form of energy-momentum conservation law play crucial roles in getting the Friedmann equations in various theories [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. ii) We also showed the form of energy-momentum conservation law depends on the energy definition, and if one uses the Komar mass, then KCL is obtained instead of OCL.…”

Implications, Consequences and Interpretations of Generalized Entropy in the Cosmological Setups

“…Now, since there are some works showing that a dark energy candidate may modify the horizon entropy [19][20][21][22][23], can one make a relation between the energy density of dark energy candidate and the general entropy relation? Here, we are going to investigate the possibility of establishing a relation between these attempts and the generalized entropy proposed by Tsallis et al [54], which is also supported by the quantum cosmology considerations [55].…”

“…in that S A is the horizon entropy, and mines sign comes from the universe expansion [9,10,[21][22][23]. Now, for a theory in which S A = S A (A), since the Cai-Kim temperature meets the [9,10,15,16], one reaches…”

“…It was also argued that a dark energy candidate, due to its unknown nature, may modify the apparent horizon entropy in various theories of gravity [19][20][21][22][23]. In fact, by decomposing ρ to ρ D +ρ o , in which ρ D denotes the energy density of dark energy candidate and ρ o includes the energy density of other parts of cosmos, using the Friedman equation (10), continuity equation (4) together with the unified first law of thermodynamics and the Clausius relation, one can obtain a new relation for the horizon entropy as…”

“…while dark energy does not interact with other parts of cosmos [21,22]. Now, by combining this equation with Eq.…”